This invention relates to a battery deterioration indicator which is used, for example, with an electronic desk top calculator with a battery as power source and indicates a battery deterioration, i.e. the remaining a battery life by detecting the battery voltage.
In recent years, a battery operated type electronic device, particularly, a device provided with integrated circuit (IC) has been designed to be operable with low power consumption. Some electronic desk top calculators with large scale integrated circuits (LSI) appearing on the market are durable for use extending from hundreds to thousands hours without replacement of batteries. In addition, some electronic watches with LSI's of the complementary symmetry metal oxide semiconductor (C-MOS) type appearing at present can even be used for years without replacing batteries. It is often experienced that such an electronic device, as mentioned above, is suddenly put in an unusable state by complete deterioration of the battery voltage, that is, consumption of the battery life during the use of it. For example, in case of an electronic desk top calculator of the long life type, for which C-MOS type LSI and a liquid crystal display device are used, the interval of time in which the battery need not be changed is long. Therefore, experiences teach us that spare batteries are seldom provided in advance. In other words, if the abovementioned battery life is exhausted during the use of the calculator, the calculating operation is compelled to be interrupted until a new battery is secured for replacement of the old one, and that is an extremely inconvenient condition.
As a solution of this problem, the following type battery life indicator has heretofore been employed. The calculator is provided with a voltage comparator capable of comparing the actual battery voltage with a predetermined limited voltage corresponding to the voltage expected to be detected just before the battery life runs out. When the battery voltage drops as low as a voltage level corresponding to the predetermined voltage, the voltage comparator operates so as to make a part of a display section of the calculator indicate a sign which indicates that the battery life will be completely consumed before long. Such a means for indication may be, for example, a means in which the individual decimal points of the display units constituting the display section are all activated, or a means in which an exclusive display region for the battery life indication is provided in the display region.
With the conventional battery life indicator as mentioned above, however, the indications are not effected till the time just before the battery life is used up. Accordingly, with the conventional indicator, it is impossible to judge how long the battery in the calculator may be used in future. Thus, the time for the battery to be changed for a new one cannot be forecast with the result that the battery life often is consumed while the calculator is being used. In such a case, using the calculator must be discontinued for a while if any spare battery is not provided for emergency. From the view point of practicality, the conventional battery life indicator is not a useful instrument.